The invention relates generally to the heating of liquids, and specifically to those devices wherein rotating elements are employed to generate heat in the liquid passing through them. Devices of this type can be usefully employed in applications requiring a hot water supply, for instance in the home, or by incorporation within a heating system adapted to heat air in a building residence. Furthermore, a cheap portable steam generator could be useful for domestic applications such as the removal of winter salt from the underside of vehicles, or the cleaning of fungal coated paving stones in place of the more erosive method by high-pressure water jet.
Of the various configurations that have been tried in the past, types employing rotors or other rotating members are known, one being the Perkins liquid heating apparatus disclosed in U.S. Pat. No. 4,424,797. Perkins employs a rotating cylindrical rotor inside a static housing and where fluid entering at one end of the housing navigates through the annular clearance existing between the rotor and the housing to exit the housing at the opposite end. The fluid is arranged to navigate this annular clearance between static and non-static fluid boundary guiding surfaces, and Perkins relies principally on the shearing effect in the liquid, causing it to heat up.
An example of a frictional method for producing heat for warming a fluid is the Newman apparatus disclosed in U.S. Pat. No. 5,392,737. Newman employs conical friction surfaces in order to generate heat, the generated heat passing into a fluid reservoir surrounding the internal elements of the device, and where the friction surfaces are engaged together by a spring and adjustment in the compression of the spring controls the amount of frictional rubbing that takes place.
Such prior attempts at producing heat have suffered for a variety of reasons, for instance, poor performance during operation, and the requirement of complicated and expensive components. Scale build-up is another cost factor should subsequent tear down and refurbishment be then needed. Similarly, because friction materials eventually wear out, they must from time-to-time be replaced.
A modem day successor to Perkins is shown in U.S. Pat. No. 5,188,090 to James Griggs. Like Perkins, the Griggs machine employs a rotating cylindrical rotor inside a static housing and where fluid entering at one end of the housing navigates past the annular clearance existing between the rotor and the housing to exit the housing at the opposite end. The device of Griggs has been demonstrated to be an effective apparatus for the heating of water and is unusual in that it employs a number of surface irregularities on the cylindrical surface of the rotor. Such surface irregularities on the rotor seem to produce an effect quite different than the forementioned fluid shearing of the Perkins machine, and which Griggs calls hydrodynamically induced cavitation. Also known as the phenomena of water hammer in pipes, the ability of being able to create harmless cavitation implosions inside a machine without causing the premature destruction of the machine is paramount. The Griggs machine may well operate with some of the developed heat through the effects of fluid shear, but nonetheless, his machine has been shown to work well and is currently known to be used in a number of applications.
An important consideration concerning machinery operating at relatively high temperature conditions is the protection of bearings and seals from premature wear. In the case of Griggs, separate detachable bearing/seal units are employed which are externally attached to the main body of the housing. As a result of such spacing, the bearing and seal members operate in a cooler environment than they otherwise might do if placed directly in the main housing body. Even so, while on the one hand such detachable bearing/seal units may well provide better performance, on the other hand, their inclusion may increase expense due to the additional complication with respect of the construction of the housing. Although by no means essential, it would be advantageous if, such bearings and seals, could be deployed in the main body of the housing.
Whereas Perkins relies on an impeller to ensure there is always a steady and continuous supply of fluid being drawn through his machine, no such impeller is included in the machine of Griggs. As a result, the Griggs machine is less flexible as it can only perform by relying on a sufficient pressure head of fluid at the input, ie. mains water pressure, or a sufficient head of pressure from above situated holding tank, in order for sufficient fluid is able to make the journey through the annular clearance between rotor and housing. In neither Griggs or Perkins is the fluid itself propelled through the clearance by the action of the rotor rotation.
There therefore is a need for a new solution for an improved mechanical fluid heater, and in-particular where the shape of the rotor operating in a similiarly shaped cavity formed by the surrounding housing causes the fluid on entering the cavity at or near to the rotational axis of the rotor to be displaced in a generally spiral trajectory and past, when incorporated on the surfaces of the rotor, a multitude of cavitation implosion zones, before reaching the periphery of the rotor. With a rotor operating as a primative form of fluid pump, less reliance is placed on having a sufficiently large head of fluid pressure at the inlet to the device.
The present invention seeks to alleviate or overcome some or all of the above mentioned disadvantages of earlier machines, in a device that is relatively simple to implement of less bulk and preferably with fewer component parts, and/or requiring fewer machining operations. The rotating member according to the invention has the potential to perform with a higher efficiency over a wider operating band, relative to the Griggs or Perkins machines because of the compactness of its rotor. As the rotor is relatively short in axial length but greater in its radial dimension, while still providing the interior volume space for deploying a series of cavitation implosion zones when included, the relative mass of the rotor as compared to Griggs or Perkins is lower allowing operation at high rotational speeds. There is a need for a new fluid heat generating device employing a rotor that can be compactly packaged in the housing, preferably avoiding the detachable bearing/seal units of Griggs for reasons of economy, operating at high speed to displaced fluid, preferably from the central intake to a peripheral exit.